[net/http] Support timeout of idle "keep-alive" connections in http.Transport

[oxtoacart]

Please answer these questions before submitting your issue. Thanks!

1. What version of Go are you using (go version)?

1.6.2

1. What operating system and processor architecture are you using (go env)?

darwin/amd64

1. What did you do?

Run the below test:

package keepalive

import (
    "net/http"
    "testing"
    "time"

    "github.com/getlantern/fdcount"
)

func TestIdle(t *testing.T) {
    _, counter, err := fdcount.Matching("TCP")
    if err != nil {
        t.Fatalf("Error getting fd count: %v", err)
    }

    maxIdleTime := 100 * time.Millisecond
    tr := &http.Transport{
    // MaxIdleTime: maxIdleTime - I'd like to be able to do this
    }
    client := http.Client{
        Transport: tr,
    }
    resp, err := client.Get("https://www.google.com/humans.txt")
    if err != nil {
        t.Fatalf("Unable to make request: %v", err)
    }
    if resp.Body != nil {
        resp.Body.Close()
    }

    time.Sleep(maxIdleTime * 2) // doesn't matter how long I sleep here, connection will never go away
    err = counter.AssertDelta(0)
    if err != nil {
        t.Errorf("Wrong number of TCP file descriptors", err)
    }
}

1. What did you expect to see?

Test passes.

1. What did you see instead?

--- FAIL: TestIdle (7.87s)
    keepalive_test.go:34: Wrong number of TCP file descriptors%!(EXTRA *errors.errorString=Unexpected TCP file descriptor count. Expected 0, have 1.

        Removed file descriptors
        -----------------------------


        New file descriptors
        -----------------------------
        keepalive 85989 ox.to.a.cart    5u    IPv4 0x2f354771863b7ca1       0t0       TCP 192.168.29.171:61989->74.125.21.99:443 (ESTABLISHED)
        )
FAIL
FAIL    command-line-arguments  7.892s

I hope to have a patch available for review later today.

[bradfitz]

Already fixed at tip. Dup of #13998. See details there.

[oxtoacart]

Awesome, thanks @bradfitz!